Hot answers tagged

34

Even "dry" concrete contains considerable water, and is a relatively good conductor. So, it's a relatively good path to ground for a person touching it, increasing the odds of a lethal shock. Generally, for something to make it into the electrical code, some number of people have probably died due to the lack of it before that happened.


33

When or is it NEC code compliant to upgrade a 2-wire circuit, by adding a third prong equipment ground from a nearby galvanized cold water pipe? Never! Article 250.118 of the National Electrical Code lists the approved methods of equipment grounding. Water piping systems are NOT listed there. Metal piping systems within buildings are required to be bonded ...


28

Let me give some framework around what ThreePhaseEel said. I can understand wondering that, since UK appliances all have fuses in their plugs, and I bet the fuses are sized to protect the appliance. The US doesn't have those. It depends on reasonably close matching between receptacle and fuse/breaker protection. Thus, the general rule is that receptacles ...


27

The key lies in the way UL tests 15A and 20A receptacles Answering this question requires a deep dive into the standard UL tests 15A and 20A receptacle devices to, namely UL 498. In particular, we have to look at the way these receptacles are tested for acceptable loading, which is governed by Section 113 of the standard. We start with the fact that a 15A ...


22

The wires in NM aren't labeled for use outside the cable jacket, and may not be the correct type for use in conduit to begin with First off, the wires inside a NM cable are not marked or labeled at all, which automatically makes them unsuitable for use in a conduit wiring method, as NEC 310.120 requires conductor insulation to be marked/labeled with the ...


17

There is one safety issue here It appears that the original installer took the ground wire from the 12/3 cable, looped it around one switch ground screw, then attached it to the other switch ground screw. This grounds the switch yokes fine, but leaves the (metal) box ungrounded save through screw threads. The solution to this is to cut off the existing ...


17

The NEC doesn't count a receptacle above 5-1/2' to satisfy the requirement - 210.52(4) Located more than 1.7 m (51⁄2 ft) above the floor The NEC doesn't have a lower limit for height, in fact 210.52(A)(3) allows floor receptacles within 18" of the wall to satisfy the requirement. (3) Floor Receptacles. Receptacle outlets in floors shall not be ...


14

You don't need GFCI receptacles anywhere. Nobody cares how you provision the GFCI protection. You are welcome to have one GFCI device and feed all the receptacles from the protected zone (LOAD) of that GFCI device. You should take the time to learn exactly how downline protection works, and then, put LOAD to good use! That will greatly reduce the cost of ...


11

The Code doesn't specify location of protection. NEC 2017 210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interrupter protection for personnel shall be provided as required in 210.8(A) through (E). The ground-fault circuit interrupter shall be installed in a readily accessible location. Th 2020 Code changes (E) to (F), ...


10

Enclosure You start with an enclosure that includes a backplate (interior panel) -- usually this is purchased separately from the enclosure itself, but the manufacturers make sizes that fit mounting holes in their enclosure. Enclosures come in many sizes, different materials, different NEMA ratings, different cover options (screw-on/hinged, handles, ...


10

It's mandatory When putting identical-appearing circuits in a conduit, you must differentiate them somehow. It's mandatory. I would not bundle them but mark them individually. Black(blue) and White(blue) for instance being the obvious pair. Bonus points: use a decent length (2") of shrinkwrap so the tape doesn't come off someday. The reason I don't ...


10

Why 20A? Receptacle design constraints, most likely The reason why general receptacle circuits top out at 20A is because the notion of a duplex receptacle doesn't work for larger plug sizes (just can't fit enough meat in there at a suitable spacing for it to work), nor does the idea of a "shared" receptacle (T-slot) that can accept 15A or 20A plugs, as well ...


10

Derailed by Derating Your plan is a non-starter, even if you overcome the fill issues you're having, because of the other limit the NEC places on conduit fill; namely, the derating factors found in 310.15(B)(3)(a) that limit ampacity based on the number of current-carrying conductors. The first two rows of the table are normally not an issue because nobody ...


10

We're reading tea leaves here to guess at NFPA's intent. NFPA writes the "model electrical code" which they offer for anyone in the world to adopt as their law. But politically, NFPA has been having a big problem. Normally NEC changes are fairly trivial in cost: Pull a neutral wire on switch loops, gosh, you're using the /3 Romex instead of the /2. It'...


10

I see two options. What I see in the US quite a bit is instead of running the plastic channels on the wall surface, people will use steel conduit. It gives kind of a rustic/industrial look. Receptacles would then be mounted in steel boxes on the wall surface as well. What is typical in Germany, where most walls are block and plaster, is that grooves are cut ...


10

No philosophy: Code is data-driven Code is the result of analysis of systematically collected data about actual electrical accidents as they happened in the field. It’s the nature of science that you must take the field data as it comes, and not try to force it to conform to some notion of what it should be. In the case of 15/20A, the data has shown that ...


9

NEC 300.4(D) covers the type of installation indicated in the question, and it applies to both AC and MC armored cable. So you'll need to use a steel guard at least 1/16" thick to protect the cable. This tip from Fine Homebuilding illustrates this type of installation. Rather than backing the molding with steel plating, they use a U-shaped channel to ...


9

Nope. Nope nope nope. You cannot use 210.12(A)(4) to put AFCI at an outlet. There are certain fairly rare cases where you can put AFCI at the first outlet. However, there is a misconception that has turned into a regular "old wives' tale", that one can skip the expensive AFCI breaker and just slap an ACFI recep at the first outlet. Oh no you can't! ...


9

They are intended to be mounted outside the box... You are correct that they are intended to be mounted to a KO (usually on the breaker box), instead of being left inside, all flop-a-dop, as yours was. You can use this unit still, although you will probably want to leave some space around it, as its further lifespan is unknown. (All MOV-based suppressors ...


8

Be sure you use a 30A double-pole breaker to adequately protect your wiring. Make sure you provide an equipment ground and use a NEMA 14-30 receptacle. The box can be metal or plastic. Some form of cable clamp is always required, it's just that most plastic boxes have an integrated clamp (that finger-trap style door). If using NM cable, The cable must be ...


8

Too many circuits per pipe All this is about the derating rules in 310.15(B)(3)(a), see ThreePhaseEel's answer. When I first saw your other question, I thought "Oh boy, I smell a too-many-circuits problem coming". I thought I should warn you to run multiple conduit, but I didn't mention it because it was out of scope. Now, if you were strictly working ...


8

That is fine. The Electrical Code is silent on the issue, except for NEC 110.3B, which requires you to obey the unit's labeling and instructions. So if they do not disallow painting the panel, then have fun. Do not cover up any labeling or numbering, and do not paint the breakers themselves. If you have a panel with no door, and you don't want to be ...


8

NEC doesn't require AFCI because it does require GFCI, and they are not the same. GFCI outlets protect against electrical shock and this is very important around water. AFCI protects against electrical arcs that come from damaged cords and bad connections. Arcing is super hot, and is responsible for electrical fires. A combination protection device could ...


8

Not sure where you got the idea that you need THWN-2, only. All you need is the W. TWN, THWN, RHW, XHW, XHHW, etc. are all perfectly fine, because they have the W that means they are waterproof, that means they can go in outdoor conduit. Most THHN is also THWN and MTW (multiply rated.) If you are in a situation where the wire temperature may be extreme you ...


8

THWN is rated for wet locations As Ecnerwal discusses. The issue is thermal The difference is at the top of Table 310.15(B)(16). THWN is allowed 75 degree C running temperature. THWN-2 is allowed 90 degrees C. THHN also is allowed 90 C Southwire is making a disclaimer: they are saying they don’t guarantee #14-10 will be THWN-2. What’s on their mind is a ...


8

The code book alone is pretty hard to understand, it's 900 pages and all written in legalese. The handbook is useful, it adds some non-legalese clarification to the NEC itself. Mike Holt's materials are great, they are made to make sense of the legalese, and they're popular for a reason. However none of the above are in any way a design guide or an ...


8

Or... just run the jacketed cable through the conduit It is permissible to run the entire, jacketed NM-B cable through the conduit. The restriction is that it takes a mighty bite out of conduit fill, because the NM-B cable must be treated the same as a round conductor of the wide dimension. This is particularly punishing when there are 2 "wires" (...


7

This answer is mostly based on the United States electrical system, and the answer may vary depending on where you are. The NEC code specifies that a solid copper wire used to connect to a ground rod must be at least either #6 or #8 gauge (depending on the size of your electrical service cable). #6 cable cable will always satisfy the sizing requirement, ...


7

The supply circuit breaker has to protect not just the cables in the wall, but also the flexible cords to the appliances. If you had 50A circuit breakers, the appliance cords would have to be rated to carry the higher fault current in the event of a short-circuit. The fault current would be several times 50A, but usually for a short time, depending on the ...


7

From the floor to 5½' The answer to your question is 5½', as per NEC 210.52 point 4: 210.52 Dwelling Unit Receptacle Outlets. This section provides requirements for 125-volt, 15- and 20-ampere receptacle outlets. The receptacles required by this section shall be in addition to any receptacle that is: (1) Part of a luminaire or ...


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